So-called rotary transfer machines are known, comprising a table rotating intermittently around a vertical or horizontal axis, holding near the periphery at equal angular distances a plurality of self-centering collets which hold the pieces to be worked. A frame placed on the periphery of said collet-holding table holds arbors constituting the operating units.
For every angular movement of the collet-holding table, i.e., at each stopping point or station, the various pieces to be worked undergo a work phase, by which each piece, at each complete rotation of the collet-holding table, undergoes all the work phases and is ejected finished.
The word "transfer" is to indicate the transfer of a piece being worked from one station to the next to perform a determined succession of work phases according to a precise plan or work cycle.
These known machines exhibit drawbacks. For example, when it is necessary to work, on both ends, a piece with a long shape which is held by self-centering collets at one end, it is not possible to assure a perfect working of the two ends since one end is not guided or in any case is held with slight rigidity because of the excessive distance from the fastening point, and is therefore subjected to vibrations and not concentric.
Further, it being necessary to go from one piece to the next, the known machines require for setting up of individual stations, and for changing of the collets and tools, operators highly skilled over a long period. The design of the known machines is such that the mobile parts, constituting the collet-holding table, control of the operating units and the arbors, constitute a set of several pieces and are of notable bulk; for which reason, strong accelerations must be avoided so as not to compromise the precision and life itself of the machine, with consequent notable reduction of rate of work and therefore of productivity. Finally, the kinematic mechanisms of known machines impose working by making cutting oil circulate as coolant for the tools and lubricant for the various mobile parts of the machine, for which reason, it is not possible, for example, to perform operations of grinding or welding or certain assemblies, or any way problems arise such as:
work hygiene because of allergy of some operators; PA1 impact on production costs because of the high cost of oils themselves; PA1 environmental damage because of high contamination caused by said oils.